1. Field of the Invention
The present invention relates to an acoustic wave device and a method of manufacturing the acoustic wave device, in particular, relates to an acoustic wave device that has a sealing portion having a hollow region above a functional region of an acoustic wave element and a method of manufacturing the acoustic wave device.
2. Description of the Related Art
An acoustic wave device is widely used as a signal filter of an electrical and electronic device using an electromagnetic wave. The acoustic wave device is used as a transmitting and receiving filter of a radio communication device such as a mobile phone or a frequency filter for visual such as a television or a videotape recorder. In the acoustic wave device, a chip such as an acoustic wave element is sealed with a sealing portion made of a resin or the like. A surface acoustic wave element is one type of an acoustic wave device, and has a structure in which an electrode exciting a surface acoustic wave such as a comb electrode is provided on a piezoelectric substrate made of LiNbO3, LiTaO3 or the like. It is necessary to form a space on the piezoelectric substrate and on the electrode, because the surface acoustic wave propagates on a surface of the piezoelectric substrate. It is necessary to seal the acoustic wave element in order to gain trust, because there is not provided a protective membrane on the piezoelectric substrate and on the electrode.
Japanese Patent Application Publication No. 9-232900, Japanese Patent Application Publication No. 2002-261582 and Japanese Patent Application Publication No. 2003-37471 disclose an art where a sealing portion is formed on a substrate having an acoustic wave element, and a Wafer Level Package (WLP) is formed, in order to reduce a cost of the acoustic wave device.
A description will be given of a method of manufacturing an acoustic wave device in accordance with a first conventional embodiment that does not have a first sealing portion 22 and a second sealing portion 24 in a cutting region. FIG. 1A through FIG. 2I illustrate a manufacturing method of the acoustic wave device in accordance with the first conventional embodiment. As shown in FIG. 1A, there is formed a comb electrode 12, a wiring 14 connected to the comb electrode 12, a metal pattern 18 in a cutting region 42 (for individuating a wafer) on a substrate 10. There is formed a protective membrane 20 on the substrate 10, the comb electrode 12 and the wiring 14. A given region of the protective membrane 20 is removed. A barrier layer 16 is formed on the wiring 14 in a penetration region 44 (a region where a penetrating electrode is to be formed). As shown in FIG. 1B, the first sealing portion 22 is formed so that a functional region 40 (a region where an acoustic wave oscillates), the cutting region 42 and the penetration region 44 (a region where a penetrating electrode is to be formed) act as a first non-covered portion 50, a second non-covered portion 52 and a third non-covered portion 54 (portions not covered with a sealing resin) respectively.
As shown in FIG. 1C, a photosensitive resin film is adhered onto the first sealing portion 22, and the second sealing portion 24 is formed. As shown in FIG. 1D, ultraviolet (UV) ray is radiated to the second sealing portion 24 with use of a mask 32. As shown in FIG. 1E, a region of the second sealing portion 24 to which the ultraviolet (UV) ray is radiated is left after a development. And the second non-covered portion 52, the third non-covered portion 54 and a cavity 60 are formed.
As shown in FIG. 2F, a penetrating electrode 28 is formed in the third non-covered portion 54. As shown in FIG. 2G, a solder ball 30 is formed on the penetrating electrode 28. As shown in FIG. 2H, a blade 36 cuts off the substrate 10 along the cutting region 42. As shown in FIG. 2I, the acoustic wave device in accordance with the first conventional embodiment is manufactured.
Next, a description will be given of a method of manufacturing an acoustic wave device in accordance with a second conventional embodiment in which the first sealing portion 22 and the second sealing portion 24 are formed in the cutting region 42. FIG. 3A through FIG. 4H illustrate a method of manufacturing the acoustic wave device in accordance with the second conventional embodiment. As shown in FIG. 3A, the first sealing portion 22 is formed so that the functional region 40 and the penetration region 44 act as the first non-covered portion 50 and the third non-covered portion 54 respectively. The first sealing portion 22 is left in the cutting region 42, being different from the first conventional embodiment shown in FIG. 1B.
As shown in FIG. 3B, a photosensitive film is adhered onto the first sealing portion 22, and the second sealing portion 24 is formed. As shown in FIG. 3C, an ultraviolet (UV) ray is radiated to the second sealing portion 24 with use of the mask 32. As shown in FIG. 3D, a region of the second sealing portion 24 to which the ultraviolet (UV) ray is radiated is left after a development. And the third non-covered portion 54 and the cavity 60 are formed. The second sealing portion 24 is left in the cutting region 42, being different from the first conventional embodiment shown in FIG. 1E.
As shown in FIG. 4E, the penetrating electrode 28 is formed in the third non-covered portion 54. As shown in FIG. 4F, the solder ball 30 is formed on the penetrating electrode 28. As shown in FIG. 4G, the blade 36 cuts off the substrate 10, the first sealing portion 22 and the second sealing portion 24 along the cutting region 42. As shown in FIG. 4H, the acoustic wave device in accordance with the second conventional embodiment is thus manufactured.
In accordance with the first conventional embodiment and the second conventional embodiment, the first sealing portion 22 has a hollow region above the functional region 40, and the second sealing portion 24 covers the hollow region. Thus, the acoustic wave element is sealed. The solder ball 30 is connected to the acoustic wave element via the penetrating electrode 28. The acoustic wave element is flip-chip mounted with the solder ball 30. Thus, an electrical signal of the acoustic wave element is output to outside.
In the first conventional embodiment, a cutting load is small when a wafer is cut into a chip, because the first sealing portion 22 and the second sealing portion 24 in the cutting region 42 are removed as shown in FIG. 2H. However, there is a case where a foreign particle is adhered to the cutting region 42 in a process between sealing the substrate 10 shown in FIG. 1E and cutting the substrate shown in FIG. 2H, if the sealing portion is not provided on the cutting region 42. For example, a metal used for the penetrating electrode 28 in FIG. 2F and a solder used for the solder ball 30 in FIG. 2G drop into the second non-covered portion 52 in the cutting region 42. The chip size may be enlarged if an interval is enlarged between the cutting region 42 and the penetrating electrode 28 in order to solve the problem.
On the other hand, in the second conventional embodiment, a metal, a solder or the like does not drop into the cutting region 42 when the penetrating electrode 28 and the solder ball 30 are formed as shown in FIG. 4E and FIG. 4F, in a case where the first sealing portion 22 and the second sealing portion 24 are left in the cutting region 42 as shown in FIG. 3A through FIG. 4E. However, the wafer is warped because of a contraction pressure of the first sealing portion 22 and the second sealing portion 24 in a heating process of hardening the first sealing portion 22 and the second sealing portion 24 or in a reflow process of the solder.